Check out the demo video at

http://www.realtraps.com/videos.htm

Interesting stuff even if you don't buy RealTraps.

bump - someone watch these and tell me what you think. Really, worth your time.

Also check out this cool link with lots of great pictures... I think there are some cool DIY options that are simple and cheap.

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Would love to see pictures of what you've made and the construction details. I've given thought to trying it by just buying some Owens 703 rigid insulation, building a simple frame and doing 2 layers with a airspace inbetween, then covering with muslin or burlap - then mounting on the wall like a picture with a spacer so there's an airspace on the wall. Then again I could just build a curtain made of R19 similar to what Ken Walden did. My research is that auralex foam does work well for high and mid freq problems but does little to nothing for low frequencies.